acoustical properties of materials chapter 8. mehta, scarborough, and armpriest : building...
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Acoustical Properties of Materials
Chapter 8
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Sound
Response of human ear to pressure fluctuations in the air caused by vibrating objects.
Sound wave is a back & forth vibratory motion passed from particle to particle through a medium
Sound frequency is the number of back and forth cycles that occur in one second ( measured as Hertz)
Audible frequency range lies between 20 Hz & 20,000 Hz
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Sound wave produced by tapping on wall
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Wavelength
Distance between peaks in a sound wave
Speed = Frequency X Wavelength
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Sound pressure (loudness) measured on decibel scale
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Types of sound: Airborne sound
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Types of sound: Structure-borne sound (impact sound)
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Airborne sound falling on a building assembly
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Airborne sound & building assembly
Sound is reflected, absorbed & transmitted Transmission rate varies with weight of assembly
Heavy-weight assemblies are poor transmitters - good insulators
Light-weight assemblies, poor insulators
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Sound transmission loss (TL): the loss of sound pressure level as sound passes through an assembly
Measured in decibels (dB) Difference in sound pressure level between
the source side and receiver side The greater the TL of a wall, the better it is as
a sound insulator TL varies with frequency, generally higher TL
with higher frequency sound
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Sound transmission loss
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Sound Transmission Class (STC)
Single number index- average of TL over frequencies ranging from 125 Hz to 4 kHz
Used to compare building assemblies
Regulated by code in some building types
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Decibel scale
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Improve STC of light weight assemblies by
Adding fibrous insulation in stud cavities
Decoupling gypsum board layer
Use multiple gypsum board layers
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Stud wall assemblies
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Resilient Channel
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Resilient Clip
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Impact Insulation Class (IIC)measure of structure-borne sound
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Sound absorption
Sound originating within room attenuated only through sound absorption
Noise reduction coefficient used to compare efficacy of materials (0-1)
Higher NRC, the more sound absorptive the material
Materials .2 NRC or higher are sound absorptive
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Ceiling tiles
Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems
© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.
Partitions: fabric-wrapped fiberglass panels absorb sound